1. Field of the Invention
The present invention relates to a cooling apparatus for a linear motor, and in particular to an improved cooling apparatus for a linear motor which can uniformly cool the whole portions of the linear motor.
2. Description of the Background Art
Differently from a general motor for performing rotary motion, a movable coil type linear motor moves directly on a straight line, and thus gets into the spotlight as a next generation motor having a high operational speed and enabling a precise positioning control.
In the movable coil type linear motor, a movable unit performs linear motion due to thrust generated between a coil unit and a permanent magnet. According to a number and position of the permanent magnets, the movable coil type linear motor is classified into an one-sided linear motor and both-sided linear motor. That is, the movable coil type linear motor is classified into the one-sided linear motor and both-sided linear motor according to whether the permanent magnets which are stators are installed at one side or both sides of the coil unit.
The linear motor relates to the both-sided type, which will now be explained.
Referring to FIG. 1, the both-sided type linear motor includes a stator 1 and a movable unit 2.
The stator 1 is composed of a xe2x80x98Uxe2x80x99 shaped stator back iron 3, and a plurality of permanent magnets 4 sequentially aligned on the facing surfaces of the stator back iron 3 in which N and S polarities are alternately generated.
The movable unit 2 includes a movable unit back iron 5 positioned at an upper opening unit side of the stator back iron 3, and a coil unit 6 installed between the permanent magnets 4 at the lower portion of the movable unit back iron 5 with a constant gap (C).
In a state where the stator 1 and the movable unit 2 are separated by the gap (C), as a predetermined distance, when current is applied to the coil unit 6, thrust is generated between the permanent magnets 4 due to the Fleming""s left-hand law, and thus the movable unit 2 performs the direct linear motion due to the thrust.
The operation of the linear motor will now be described. When a control device (not shown) applies current to the coil unit 6, the current is transferred to a coil of the coil unit 6, and magnetic field and thrust are generated between the permanent magnets 4 and the coil unit 6 installed inside the stator back iron 3, thereby moving the movable unit 2 in the front/rear direction. Here, the control device (not shown) controls a movement speed of the movable unit 2 and thrust by the movement according to a winding number of the coil and the supply current.
Since the movable unit 2 repeatedly moves at one side of the stator 1, relatively high heat is generated between the coil unit 6 and the permanent magnets 4 due to the current flowing through the coil. The heat changes magnetic field properties of the stator 1 and the movable unit 2. As a result, properties of the linear motor are varied not to enable precise controlling.
A cooling apparatus for the linear motor has been suggested to solve the foregoing problem.
As one example of the cooling apparatus for the linear motor, as shown in FIG. 1, at least one air hole 7 is formed in the movable unit back iron 5 in a longitudinal direction, and a plurality of air nozzles 8 are formed in the air hole 7 at predetermined intervals, and opened toward the stator 1, for injecting cooling air flowing along the air hole 7 into the gap (C) of the permanent magnets 4 and the coil unit 6.
When a temperature of the linear motor exceeds a predetermined value, the control device operates an air pump to supply the cooling air to the air hole 7. The air is supplied to the gap (C) between the permanent magnets 4 and the coil unit 6 through the air nozzle 8 to cool the permanent magnets 4 and the coil unit 6, thereby maintaining the linear motor at an appropriate temperature.
The conventional cooling apparatus for the linear motor supplies the cooling air to the gap (C) between the permanent magnets 4 and the coil unit 6, to cool the permanent magnets 4 and the coil unit 6. However, the cooling air is supplied merely from the upper air nozzles 8, the gap (C) receiving the cooling air is small, and thus the cooling air does not reach into the lower end portion of the gap (C). Accordingly, the linear motor does not have a uniform temperature in the whole portions, which results in mis-operation of the linear motor and low reliability of the cooling apparatus for the linear motor.
Accordingly, it is an object of the present invention to provide a cooling apparatus for a linear motor which can uniformly cool the whole portions of the linear motor.
In order to achieve the above-described object of the invention, there is provided a cooling apparatus for a linear motor comprising:
a xe2x80x98Uxe2x80x99 shaped stator back iron;
a stator having a plurality of permanent magnets installed on inner facing surfaces of the stator back iron;
a coil unit positioned between the stator and the permanent magnets with a predetermined gap;
a movable unit having a movable unit back iron fixed on the coil unit, the movable back iron having at least one first air hole formed therein in a longitudinal direction and a first air nozzle linked to the first air hole for injecting cooling air from the top portion of the coil unit to the bottom portion; and
a frame aligned at the lower portion of the coil unit having a second air hole formed in a longitudinal direction thereof for receiving the cooling air and a second air nozzle linked to the second air hole for injecting the cooling air from the bottom portion of the coil unit to the top portion.
Preferably, the frame has a xe2x80x98Uxe2x80x99 shape, both side vertical units of which being connected respectively to the front and rear portions of the movable unit back iron, thereby injecting cooling air from both sides of the second air hole and the first air hole.
Preferably, the second air hole is formed at one center portion of the frame, and the second air nozzle is protruded from both sides of the second air hole, for injecting the cooling air into both sides of the coil unit.